1. Field of the Invention
The present invention relates to a screw, in particular to a screw with lower screwing torque and higher screwing speed.
2. Description of the Related Art
A conventional screw 1 disclosed in FIG. 1 generally comprises a head 11, a shank 12 extending therefrom, and a set of threads 13 spirally arranged on the shank 12 along a shank axis α. While initially directing the shank 12 toward an object 4 (i.e. chipboard), users impart a torque force upon the head 11 to drive the thread 13 rotarily cutting the object 4 and progressively drill the shank 12 into the object 4. However, when driving the screw 1 into an object, debris to be extruded out of a channeled hole acts as a counter-acting force against the driven threads 13, which increases the amount of labor and time required to drive the screw 1.
A fastener device 2 of a prior art for engaging an initial threaded female member or workpiece, disclosed by H. F. Phipard, Jr. in U.S. Pat. No. 3,454,070, essentially includes a set of upper thread(s) 21 and a shank 22 tapered to a tip end at 23. The prior art further presents that distal threads 24 proximate to the tip 23 are clearly planar as shown in FIG. 2, namely to juxtaposedly align each planar surface 241 on each distal thread. Further, it distinctly performs in FIG. 3 that the general formation of thread peak on the threads 21 provides with a thread width W1 consistent with that W2 of the plane surface on the distal threads 24 with respect to a contour line β designating at a certain height range.
Still further, when initially driving the screw fastener 2 into a pre-drilled hole of a workpiece 4, such plane surfaces 241 substantially substitute deflecting debris 5 of the workpiece aside for exerting themselves to chip those debris, so as to create an interior track inside the workpiece and predetermine the range of clearances. However, such debris would interfere with the advance of the screw 2 when it turns to immediately surround the shank 22, which may incur a larger drilling torque. In the subsequently gradual drilling toward the upper threads 21 along the track as arrowed, the debris 5 inevitably become jam or accumulated within the workpiece 4 since the configuration of the equal thread width (W1=W2) renders the upper threads 21 densely engage with the tracks and has rather no space formed therebetween to acceptably extrude redundant debris 5 out of the workpiece. Hence, Phipard's fastener potentially results of a progressive increment of the screwing resistance and drilling torque during the travel of the screw 2 through the workpiece and even causes the destruction of the workpiece 4. It still fails to overcome the deficiencies of the conventional screw 1.